The 2FA Email setting is only available for the Devolutions Password Server. It will request the user's email account as its second component to access the data source.
If you have selected the option Required in the 2FA usage option every user will automatically have a 2FA request when logging in, it will not be necessary to edit each and every one of your users as long as they have an email address set in their User setting.
If you select the option Optional per User in the 2FA usage option you will have to proceed to a set up for each user you wish to use the 2FA.
For this option to be valid you will have to configure the Server and the User.
See 2FA Email for more information on the settings.